The present invention relates to a method and apparatus for inspecting, in a process of manufacturing a semiconductor device, foreign particles or a state of occurrence of defects, which method and apparatus is relevant to a step of detecting, analyzing, and taking measures against a foreign particle on a thin film substrate, semiconductor substrate, photomask, and other objects that are produced in manufacture of a semiconductor chip or a liquid crystal product, as well as a defect in a circuit pattern in the thin film substrate, semiconductor substrate, photomask and others.
In a process of producing a semiconductor device, a foreign particle present on a semiconductor substrate or a wafer leads to a defect such as defective insulation of wiring and short-circuit. With a recent trend of miniaturization of semiconductor devices, a minute foreign particle could be a cause of defective insulation of a capacitor or damage of a gate oxide film or others. Such a foreign particle is produced and introduced in various ways. For instance, the foreign particle may come from a movable portion in a feeding device or a human body, may be generated as a reaction product in a processing apparatus during a process using a process gas, or may come from chemicals or materials.
Similarly, in a process of producing a liquid crystal display element, when a defect is caused in a pattern by the foreign particle introduced in the above-described manner, the finished display element does not work. With a process of producing a printed circuit board or a printed wiring board, the circumstances is the same, namely, introduction of a foreign particle causes a short-circuit in a pattern or a bad connection. Hence, in manufacture of semiconductor devices, one (or more in some situations) foreign particle inspecting apparatus is disposed in each production line so as to detect a foreign particle at an early stage and feed back a result of the detection, in order to improve the yield rate.
One of techniques of this kind to detect a foreign particle on a semiconductor substrate is disclosed in JP-A-62-89336, which teaches to irradiate a semiconductor substrate with a laser beam and detect scattered light from a foreign particle adhering to the semiconductor substrate. The result of the inspection is compared with a result of an inspection last performed for the same kind of semiconductor substrate, so as to eliminate the possibility of misdetection of a pattern and enable a highly sensitive and reliable inspection of foreign particle defects. Disclosed in JP-A-63-135848, there is known another technique in which a semiconductor substrate is irradiated with a laser beam and scattered light from a foreign particle adhering to the semiconductor substrate is detected, and the detected foreign particle is analyzed by a method such as laser photoluminescence spectroscopy and secondary X-ray analysis (XMR).
As a technique to inspect foreign particles as mentioned above, there is known a method such that a wafer is irradiated with coherent light, and light emitted from a repetitive or periodic pattern on the wafer is removed by a spatial filter so that a foreign particle and a defect that are irregular or not periodic are emphasized to be detectable. Further, JP-A-1-117024 discloses a foreign particle inspecting apparatus where light is emitted toward a circuit pattern on a wafer in a direction 45-degree inclined with respect to directions of straight segments of principal groups in the circuit pattern and the zeroth-order diffraction light from the straight segments of the principal group is prevented from entering an aperture of an objective lens. The publication JP-A-1-117024 also teaches to block light emitted from straight segments of the other group than those of the principal groups by a spatial filter.
A technique related to an apparatus and method for inspecting a defect such as presence of a foreign particle is disclosed in JP-A-1-250847 and JP-A-2000-105203. The publication JP-A-2000-105203 teaches to change a pixel size at which detection is performed, by enabling switching associated with the detection optical system used for the detection, and to inspect a foreign particle by illuminating a substrate with light condensed in one direction. JP-A-2001-60607 discloses a technique to measure a size of a foreign particle.
However, any of the above-described conventional techniques does not succeed to detect with ease, at a high speed, and with a high sensitivity, a minute foreign particle or defect on a substrate on which a periodic pattern and a non-periodic pattern are present in a mixed manner. That is, the conventional techniques can not solve a problem that at a portion other than a periodic pattern such as memory cell portion, the detection sensitivity is low, or a minimum particle size detectable is large. Further, according to the conventional techniques, the detection sensitivity for a minute foreign particle or a defect on the order of 0.1 μm in an area where the pattern density is high is low. Still further, the detection sensitivity is low for a foreign particle or a defect that causes a short-circuit between wires, and for a foreign particle in the form of a thin film. The conventional technique disclosed in JP-A-2001-60607 has drawbacks that the measuring accuracy and precision for a foreign particle or a defect is low, and the detection sensitivity for a foreign particle on a wafer coated with a thin transparent film is low.